Digital cameras often comprise elements enabling variable focus distances. Moreover, various mobile apparatuses, such as smartphones and tablet computers, may incorporate miniaturized digital camera modules by which the user may capture still pictures and/or videos. Also in such camera modules, the focus distance may be variable.
The variable focus distance may be implemented e.g. by means of a focus lens assembly in which one or more focus lenses are movable along an optical axis in relation to an image sensor, driven by means of an actuator. For exposure of a frame for still picture or video sequence, the focus lens assembly may be driven to a predetermined frame focus position to produce a focused image of an object on the image sensor.
With a movable focus lens assembly, the image quality of an exposed frame may depend on the stability of the focus lens assembly in relation to the image sensor during the exposure of the frame.